Horton

Re: Statistics Import and Export

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Bruce Momjian <bruce@momjian.us>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>, Corey Huinker <corey.huinker@gmail.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2024-03-28T06:32:09Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Change pg_dump default for statistics export.

  2. pg_dump: Adjust reltuples from 0 to -1 for dumps of older versions.

  3. vacuumdb: Don't skip empty relations in --missing-stats-only mode.

  4. pg_dump: Fix query for gathering attribute stats on older versions.

  5. Prevent redeclaration of typedef TocEntry.

  6. Remove unused function parameters in pg_backup_archiver.c.

  7. pg_dump: Retrieve attribute statistics in batches.

  8. pg_dump: Reduce memory usage of dumps with statistics.

  9. Skip second WriteToc() call for custom-format dumps without data.

  10. Add relallfrozen to pg_dump statistics.

  11. Matview statistics depend on matview data.

  12. Add pg_dump --with-{schema|data|statistics} options.

  13. Stats: use schemaname/relname instead of regclass.

  14. CREATE INDEX: do update index stats if autovacuum=off.

  15. Don't convert to and from floats in pg_dump.

  16. CREATE INDEX: don't update table stats if autovacuum=off.

  17. Organize and deduplicate statistics import tests.

  18. Address stats export review comments.

  19. Address stats import review comments.

  20. Add relallfrozen to pg_class

  21. Fix pg_strtof() to not crash on NULL endptr.

  22. Use attnum to identify index columns in pg_restore_attribute_stats().

  23. pg_dump: prepare attribute stats query.

  24. Avoid unnecessary relation stats query in pg_dump.

  25. Remove redundant pg_set_*_stats() variants.

  26. Do not use in-place updates for statistics import.

  27. Fix confusion about data type of pg_class.relpages and relallvisible.

  28. Documentation fixups for dumping statistics.

  29. Trial fix for old cross-version upgrades.

  30. Transfer statistics during pg_upgrade.

  31. Lock table in ShareUpdateExclusive when importing index stats.

  32. Use in-place updates for pg_restore_relation_stats().

  33. Improve error message for replication of generated columns.

  34. pg_dump: Add dumpSchema and dumpData derivative flags.

  35. Disallow modifying statistics on system columns.

  36. Add missing CommandCounterIncrement() in stats import functions.

  37. Add functions pg_restore_relation_stats(), pg_restore_attribute_stats().

  38. Documentation fixup.

  39. Add functions pg_set_attribute_stats() and pg_clear_attribute_stats().

  40. Change pg_*_relation_stats() functions to return type to void.

  41. Disable autovacuum for tables in stats import tests.

  42. Allow pg_set_relation_stats() to set relpages to -1.

  43. Fixup for pg_set_relation_stats().

  44. Create functions pg_set_relation_stats, pg_clear_relation_stats.

  45. Add memory/disk usage for Window aggregate nodes in EXPLAIN.

  46. Improve performance of dumpSequenceData().

  47. Add INJECTION_POINT_CACHED() to run injection points directly from cache

  48. Improve performance of binary_upgrade_set_pg_class_oids().

  49. Improve assertion in mdwritev()

  50. CREATE INDEX: do not update stats during binary upgrade.

  51. Redefine pg_class.reltuples to be -1 before the first VACUUM or ANALYZE.

Hi Tom,

Comparing the current patch set to your advice below:

On Tue, 2023-12-26 at 14:19 -0500, Tom Lane wrote:
> I had things set up with simple functions, which
> pg_dump would invoke by writing more or less
> 
>         SELECT pg_catalog.load_statistics(....);
> 
> This has a number of advantages, not least of which is that an
> extension
> could plausibly add compatible functions to older versions.

Check.

>   The trick,
> as you say, is to figure out what the argument lists ought to be.
> Unfortunately I recall few details of what I wrote for Salesforce,
> but I think I had it broken down in a way where there was a separate
> function call occurring for each pg_statistic "slot", thus roughly
> 
> load_statistics(table regclass, attname text, stakind int, stavalue
> ...);

The problem with basing the function on pg_statistic directly is that
it can only be exported by the superuser.

The current patches instead base it on the pg_stats view, which already
does the privilege checking. Technically, information about which
stakinds go in which slots is lost, but I don't think that's a problem
as long as the stats make it in, right? It's also more user-friendly to
have nice names for the function arguments. The only downside I see is
that it's slightly asymmetric: exporting from pg_stats and importing
into pg_statistic.

I do have some concerns about letting non-superusers import their own
statistics: how robust is the rest of the code to handle malformed
stats once they make it into pg_statistic? Corey has addressed that
with basic input validation, so I think it's fine, but perhaps I'm
missing something.

>  As mentioned already, we'd also need some sort of
> version identifier, and we'd expect the load_statistics() functions
> to be able to transform the data if the old version used a different
> representation.

You mean a version argument to the function, which would appear in the
exported stats data? That's not in the current patch set.

It's relying on the new version of pg_dump understanding the old
statistics data, and dumping it out in a form that the new server will
understand.

>   I agree with the idea that an explicit representation
> of the source table attribute's type would be wise, too.

That's not in the current patch set, either. 

Regards,
	Jeff Davis